Changes the agency will require before allowing flights to resume include having airlines with 787s install containment and venting systems for the batteries.

The Federal Aviation Administration approved Boeing Co.'s proposed fix for the lithium-ion battery systems on its 787 Dreamliner passenger jets, which have been grounded since January, clearing the way for a return to flight.

The FAA said it will require airlines flying 787s to install containment and venting systems for the batteries. The agency will also instruct carriers to replace the batteries and their chargers with modified components.

Boeing has delivered 50 787s to eight airlines worldwide, including United Airlines, the only U.S. carrier that has 787s in its fleet.

To make sure the work gets done, the FAA has teams of inspectors at the modification sites. The FAA said it would not allow any modified 787 to take to the sky until it approves the work.

"Safety of the traveling public is our No. 1 priority," U.S. Transportation Secretary Ray LaHood said in a statement. "These changes to the 787 battery will ensure the safety of the aircraft and its passengers."

Mike Sinnett, Boeing's chief project engineer for the 787 program, said in a teleconference that the company will send kits to airlines in order to fix the plane, but that it also has 10 teams around the world ready to help with the installation.

The fix, he said, would take about five days to finish for each plane. But he stopped short of saying when the first 787 would reenter service.

"The rest is really up to the airlines," Sinnett said.

United Airlines said this month that it plans to resume 787 flights May 31.

Boeing and the FAA said they will support international aviation authorities that are working toward finalizing their own acceptance procedures of the 787 design change.

"It's good news, of course," said Scott Hamilton, an aviation industry consultant and managing director of Leeham Co. in Issaquah, Wash. "It remains to be seen how quickly the Japanese and European agencies follow suit."

The FAA's move to get the 787 fleet airborne again comes two weeks after Boeing completed a certification demonstration flight with a crew of 11 on board that took 1 hour 49 minutes.

"FAA approval clears the way for us and the airlines to begin the process of returning the 787 to flight with continued confidence in the safety and reliability of this game-changing new airplane," Boeing Chief Executive Jim McNerney said in a statement. "The promise of the 787 and the benefits it provides to airlines and their passengers remain fully intact as we take this important step forward with our customers and program partners."

Boeing and FAA officials have been busy addressing concerns about the company's new flagship jet, which has been grounded worldwide since Jan. 16 after two overheating incidents within two weeks involving the battery systems.

Aerospace analysts have estimated that the three-month grounding has cost Boeing hundreds of millions of dollars.

On March 14, the Chicago company unveiled a plan to fix the 787 battery system. It involves insulating and spacing out parts in the battery unit, reducing charging levels so the battery cannot be overcharged and enclosing the lithium-ion batteries in stainless-steel cases so that little oxygen can get at them.

The redesign removes any risk of a fire breaking out within the battery system, the company said.

All 787s were grounded after a battery fire broke out Jan. 6 on a 787 operated by Japan Airlines at Boston's Logan International Airport and a second battery incident occurred 10 days later on an All Nippon Airways flight in Japan.

The 787's battery system, which is made in Japan by Kyoto firm GS Yuasa Corp., contains a cluster of eight individual cells packaged together in one box.

The National Transportation Safety Board has been investigating the matter, as have officials from Boeing, the FAA, the Navy, Japan and France. Not one of them has found a cause for the incidents.

Boeing said its team spent more than 100,000 work hours developing test plans, building test rigs, conducting tests and analyzing the results to ensure the proposed solutions met all requirements.

Boeing has taken a total of 890 orders for the Dreamliner from airlines and aircraft leasing firms around the world. Depending on the version ordered, the price ranges from $206.8 million to $243.6 million per jet.

The Chicago company currently is making five Dreamliners a month, and it plans to reach 10 a month late this year.

Boeing said in a recent financial statement that it expected "no significant financial impact" from the 787 grounding this year, even though it will not deliver any new 787s as long as the plane is grounded. The company says it expects to complete all planned 2013 deliveries by the end of the year.

Despite the problems, Boeing's stock has risen 14% this year. Shares rose $1.84, or 2.1%, to $87.96 on Friday.